A wide variety of different electric motors is installed in a motor vehicle. Such an electric motor may drive, for example, a valve, a flap, a pump, a fan, a power window, a seat adjuster, a windshield wiper, or another element on board the motor vehicle. The electric motor is equipped with a controller in order, for example, to control a direction of rotation or a rotational speed as a function of existing requirements. The controller often includes a programmable microcomputer having a data interface for exchanging control data. The microcomputer then controls the electric motor with the aid of a power circuit.
In order to protect the controller, the electric motor, or an electrical supply network, on which the controller and the electric motor are operated, from damage, the controller may include one or multiple protective circuits, which limit or shut off a current when it is determined that a fault condition exists. For example, a current through the electric motor may be shut off if it was detected that the supply voltage of the controller or of the electric motor has the wrong polarity. In another specific embodiment, the protective circuit may be provided in order to limit a current through the electric motor, in particular during a start-up phase.
Such a protective circuit includes a field effect transistor having a gate. In order to switch on the field effect transistor, voltage at the gate must exceed a predefined plateau voltage. If at least the plateau voltage is present, a leakage current flows from the gate through the field effect transistor, so that a certain output is required in order to hold the gate above the plateau voltage.